Steven F. Ashby Center for Applied Scientific Computing Month DD, 1997

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Paper Presentation - Micropolygon Ray Tracing
With Defocus and Motion Blur -
Qiming Hou, Hao Qin, Wenyao Li, Baining Guo, Kun
Zhou Presenter Jong Hyeob Lee 2010. 10. 28
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Micropolygon

• What is a micropolygon?
• Polygon
  Micropolygon

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Defocus and Motion Blur
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Rasterization vs Ray Tracing

• Tracing a ray is slower than rasterizing a pixel.
• Every ray returns something useful. Rasterization
  waste time on not-covered or occluded pixels.
• Tradeoff between per-operation cost and useful
  operation percentage.
• Stochastic sampling favors ray tracing.

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Goal

• A 4D micropolygon ray tracing
• Performs up to an order of magnitude faster than
  rasterization.
• Eliminates the quality-performance tradeoff in
  defocus and motion blur rendering.

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Related Works

• Micropolygon
• Reyes Cook et al. 1987
• RenderAnts Zhou et al. 2009
• Defocus and Motion Blur
• Adaptive sampling Hachisuka et al. 2008
• Hyper-trapezoids
• Collision detection Hubbard 1995

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Overview

• Hyper-trapezoid
• BVH Construction
• Ray Generation
• BVH Traversal

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Overview

• Hyper-trapezoid
• BVH Construction
• Ray Generation
• BVH Traversal

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Hyper-trapezoid

• A hyper-trapezoid is
• Two faces at T0, T1 interpolated linearly
  across T

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Hyper-trapezoid

• Axis-aligned bound box Bounding box based
  hyper-trapezoid

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Hyper-trapezoid

• 4D OBB hyper-trapezoids
• The T0 and T1 faces are 3D OBB, analogous to 3D
  Hyper-trapezoids with 2D Bouding Box faces.

T1
T0
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Comparisons with AABB

• Test scenes (Furball, Ladybug, Fairy, Car)

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Comparisons with AABB
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Overview

• Hyper-trapezoid
• BVH Construction
• Ray Generation
• BVH Traversal

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BVH Construction

• Basic topology is the same as general BVH.

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BVH Construction

• Build process
• Top level BVH
• In-grid level BVH
• Compute bounding volume

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BVH Construction

• Top level BVH
• Unit Micropolygon grid
• Split strategy Surface Area Heuristic
• Termination criterion One gird in every node

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BVH Construction

• In-grid level BVH
• Unit Micropolygons
• Split strategy Parametric space mid-split
• Termination criterion Less than 8 micropolygons
  in a node

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BVH Construction

• Compute bounding volume
• Compute grid-level orientation
• Bottom-up merge use the orientation that
  results in smaller surface area.
• Top-down simplify use parent nodes orientation
  if surface area isnt increased too much.

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Overview

• Hyper-trapezoid
• BVH Construction
• Ray Generation
• BVH Traversal

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Ray Generation

• Reducing the alias
• Lens permutation magic square
• Time permutation magic square shuffled and
  shifted per-pixel

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Overview

• Hyper-trapezoid
• BVH Construction
• Ray Generation
• BVH Traversal

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BVH Traversal Ray and OBB

• Transforming rays into per-box local frame.

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BVH Traversal Ray and OBB

• Transforming rays into per-box local frame.

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BVH Traversal - Micropolygon

• Use a rasterization-like method to compute
  pseudo-intersections for micropolygons.
• Project micropolygon to view plane.
• Use even-odd rule to test it.

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Comparison with Rasterization

• Better quality

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Comparisons with AABB

• Test scenes (Furball, Ladybug, Fairy, Car)

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Comparison with Rasterization

• Faster sampling time

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Result Total rendering time
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Conclusion

• The first time ray tracing is faster than
  rasterizaion.
• A novel acceleration structure based on oriented
  hypertrapezoid.
• Limitation
• Inefficiency of transparency handling
• The BVH is not effective when tracing rays
  inside objects over rasterization methods.

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QA

• Thank you.